As semiconductor devices continue to decrease in size, noise isolation becomes increasingly difficult to maintain. A conventional method of controlling noise isolation has been the manipulation of the semiconductor substrate resistivity. Typically, higher substrate resistivity results in higher noise isolation between devices or terminals within a device. Thus, high resistivity substrates are becoming more popular in applications requiring a high degree of intra-substrate noise isolation. However, because high resistivity substrates have very low doping concentrations, large electric fields can form between points having high potential differences in the substrate, such as between the collector and emitter of bipolar junction transistors. For example, voltage differences between an emitter and collector can deplete the substrate of charge carriers, significantly increasing the electric field in the substrate, causing DC breakdown.
In addition, conventional external interconnection of bipolar devices typically includes wire bonding topside contacts to a leadframe several millimeters away. However, such wirebonds and long interconnect paths tend to have unacceptably high resistance and/or inductance, thus, necessitating multiple wires or connections.